Figure 1817

Diagram of a type II alveolar cell and electron micrograph of lamellar bodies, a. Surfactant is an oily mixture of proteins, phospholipids, and neutral lipids that are synthesized in the rER from precursors in the blood. These precursors are glucose, fatty acids, choline, and amino acids. The protein constituents of surfactant are produced in the rER and stored in the cytoplasm within lamellar bodies, which are discharged into the lumen of the alveolus. With the aid of surfactant

protein, surfactant is distributed, on the surface of epithelial cells lining the alveolus, as a thin film that reduces the surface tension, b. Higher-magnification electron micrograph showing the typical lamellar pattern of the secretory vesicles of type II alveolar cells. These vesicles contain the pulmonary surfactant precursor proteins. x38,000. (Courtesy of Dr. A. Mercuri.)

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